§ 141.82 Description of corrosion control treatment requirements.

This section sets forth the requirements applicable to systems and states in the designation of optimal corrosion control treatment for a system that is optimizing or reoptimizing corrosion control treatment. Each system must complete the corrosion control treatment requirements in this section as applicable to such system under § 141.81.

(a) System recommendation regarding corrosion control treatment for systems that do not contain lead service lines and systems with lead service lines that do not exceed the lead action level. (1) Any system under this paragraph (a) without corrosion control treatment that is required to recommend a treatment option in accordance with § 141.81(e) must, based on the results of lead and copper tap sampling and water quality parameter monitoring, recommend designation of one or more of the corrosion control treatments listed in paragraph (c)(1)(i) of this section. Small community water systems and non-transient non-community water systems that exceed the copper action level must comply with this paragraph (a)(1). The State may require the system to conduct additional water quality parameter monitoring to assist the State in reviewing the system's recommendation.

(2) Any small community water system or non-transient non-community water system in this paragraph (a) without corrosion control treatment that chooses to pursue a small water system compliance flexibility option and is required to recommend an option in accordance with § 141.81(f) must, based on the results of lead tap sampling and water quality parameter monitoring, recommend designation of one of the options listed in § 141.93. Systems with no lead service lines that exceed the lead action level and select corrosion control under § 141.93(a)(2) must recommend designation of one or more of the corrosion control treatments listed in paragraph (c)(1) of this section as the optimal corrosion control treatment for that system.

(3) Any system under this paragraph (a) that exceeds the lead action level and selects corrosion control under § 141.93(a)(2) must recommend designation of one or more of the corrosion control treatments listed in paragraph (c)(1)(i) of this section as the optimal corrosion control treatment for that system. A corrosion control study under paragraph (c) of this section is not required for medium and small systems that exceed the lead trigger level but do not exceed the lead and copper action levels, unless required by the state.

(4) Any small community water system or non-transient, non-community water system with corrosion control treatment that that exceeds the lead action level and selects corrosion control under § 141.93(a)(2) must recommend designation of one or more of the corrosion control treatments listed in paragraph (c)(2) of this section as the optimal corrosion control treatment for that system.

(5) States may waive the requirement for a system to recommend OCCT if the State requires the system, in writing, to complete a corrosion control study within 3 months after the end of the tap sampling period during which the exceedance occurred. Such systems shall proceed directly to paragraph (c) of this section and complete a corrosion control study.

(b) State decision to require studies to identify initial optimal corrosion control treatment and re-optimized optimal corrosion control treatment except for large systems and small and medium systems with lead service lines that exceed the lead action level. Corrosion control treatment studies are always required for large systems that exceed the lead action level, large water systems without corrosion control treatment with 90th percentile results that exceed either the lead practical quantitation level of 0.005 mg/L or the copper action level, medium sized systems with lead service lines that exceed the lead action level, and small systems with lead service lines that exceed the lead action level and select the corrosion control treatment option under § 141.93(a).

(1) The State may require any small or medium-size system without corrosion control that exceeds either the lead or copper action level to perform corrosion control treatment studies under paragraph (c)(1) of this section to identify optimal corrosion control treatment for the system.

(2) The State may require any small or medium-size system without corrosion control that exceeds the lead trigger level but not the lead or copper action level to perform corrosion control treatment studies under paragraph (c)(1) of this section to identify optimal corrosion control treatment for the system. This corrosion control treatment shall be installed if the lead or copper action level is subsequently exceeded.

(3) The State may require any small or medium-size water systems with corrosion control treatment exceeding either the lead trigger level or copper action level to perform corrosion control treatment studies under paragraph (c)(2) of this section to identify re-optimized optimal corrosion control treatment for the system (i.e., optimal corrosion control treatment after a re-optimization evaluation).

(c) Performance of corrosion control studies. (1) Water systems without corrosion control treatment that are required to conduct corrosion control studies must complete the following:

(i) Any water system without corrosion control treatment must evaluate the effectiveness of each of the following treatments, and if appropriate, combinations of the following treatments to identify the optimal corrosion control treatment for the system:

(A) Alkalinity and pH adjustment;

(B) The addition of an orthophosphate- or silicate-based corrosion inhibitor at a concentration sufficient to maintain an effective corrosion inhibitor residual concentration in all test samples;